Recently, a GaN-based compound semiconductor has become a focus of attention as a semiconductor material of the light-emitting element of short wavelength light. The GaN-based compound semiconductor is formed by a metal organic chemical vapor deposition method (MOCVD method), a molecular beam epitaxy method (MBE method) or the like on a sapphire single crystal or other various oxides or group III-V compounds provided as a substrate.
In a semiconductor light-emitting element using the GaN-based compound semiconductor, a laminated semiconductor layer having a light-emitting diode (LED) structure constituted by an n-type semiconductor layer, a light-emitting layer and a p-type semiconductor layer was formed on a substrate and an electrode having optical transparency (transparent electrode) was formed on the p-type semiconductor layer on the top portion, thereby extracting emitted light via the transparent electrode.
On some portions of the transparent electrode, which connect to bonding wires made of Au (gold), bonding pads made of Au or an alloy containing Au were formed. Since these bonding pads cut off light from the light-emitting layer, it was impossible to extract emitted light from the light-emitting layer through the portions on the transparent electrode where the bonding pads were formed.
Further, in the semiconductor light-emitting element, light traveling toward the transparent electrode and light traveling toward the substrate are emitted from the light-emitting layer. Of these, the light traveling toward the substrate was absorbed by a package on which the substrate and the semiconductor light-emitting element were mounted or by an adhesive that bonds the semiconductor light-emitting element to the package, and therefore, the light traveling toward the substrate was difficult to be extracted to the outside.
In contrast, by an FC (flip-chip bonding) mount technology, in which a semiconductor light-emitting element formed on a substrate that is transparent to light emission wavelength is reversed and mounted on a circuit board (submount) or a package, light is extracted from a substrate side where no electrodes are formed to avoid light exclusion by electrodes, and thereby light extraction efficiency is improved.
Moreover, since, in the semiconductor light-emitting element and the circuit board (submount), the electrodes of the semiconductor light-emitting element and pads of wiring on the circuit board (submount) are connected with each other via bumps made of Au or the like, an area on the circuit board (submount) required for mounting of the semiconductor light-emitting element is reduced and mounting can be performed in high density, with high reliability in connection compared to the method of connection with bonding wires.
By the way, for using the FC mount technology, the semiconductor light-emitting element is configured such that both of the positive electrode and the negative electrode are taken out from a front surface side of the laminated semiconductor layer, which is opposite to the substrate, and a reflecting layer made of Ag (silver) or the like, which has high reflectance to the light emission wavelength, is provided on the front surface side of the laminated semiconductor layer. Consequently, the light traveling toward the electrodes is reflected and extracted from the substrate side, and accordingly, the light extraction efficiency is further improved.
In the Patent Document 1, a semiconductor light-emitting element is disclosed, in which a first conduction type semiconductor layer, a light-emitting layer, and a second conduction type semiconductor layer are laminated in this order, and an electrode connected to the second conduction type semiconductor layer includes a lower layer conductive oxide film, an upper layer conductive oxide film which is formed on the lower layer conductive oxide film so that a part of a front surface of the lower layer conductive oxide film may be exposed, and a metal film disposed only on the upper layer conductive oxide film. The lower layer conductive oxide film functions as a non-reflective film at the region where the metal film is not disposed, and the upper layer conductive oxide film functions as a reflective film having high reflectance to the light emission wavelength at the region where the metal film is disposed.